Adrenergic receptors (also called adrenoceptors) are the receptors for the catecholamines adrenaline and noradrenaline (called epinephrine and norepinephrine in the United States). Adrenaline and noradrenaline play important roles in the control of blood pressure, myocardial contractile rate and force, airway reactivity, and a variety of metabolic and central nervous system functions.
 
Adrenergic receptors are members of the G-protein coupled receptor (GPCR) superfamily of membrane proteins. They share a common structure of seven putative transmembrane domains, an extracellular amino terminus, and a cytoplasmic carboxyl terminus.

Adrenoceptors are divided into three types: α₁, α₂ and β-adrenoceptors. Each type is further divided into at least three subtypes: α_1A, α_1B, α_1D, α_2A, α_2B, α_2C, β₁, β₂, β₃.^1,2 Adrenoceptors are expressed in nearly all peripheral tissues and in the central nervous system.^1,2
 
β₂-Adrenoceptors are mainly postsynaptic receptors. They are expressed on a number of tissues including blood vessels, bronchi, gastrointestinal tract (GIT), skeletal muscle, liver and mast cell.³ Functional β₂-adrenoceptors were also found on lymphocytes, macrophages and neutrophils.^4,5 They are also the only β-adrenoceptor subtype expressed in keratinocytes, fibroblasts and melanocytes.³ Activation of β₂-adrenoceptors results in vasodilation, relaxation of the GIT, inhibition of histamine release from mast cells and bronchodilation. Selective agonists of β₂-adrenoceptors are used to treat asthma and other related bronchospastic conditions such as Chronic obstructive pulmonary disease (COPD).⁵